Substrate-borne vibration in Pacific field cricket courtship displays

Abstract

While thought to be widely used for animal communication, substrate-borne vibration is relatively unexplored compared to other modes of communication. Substrate-borne vibrations are important for mating decisions in many orthopteran species, yet substrate-borne vibration has not been documented in the Pacific field cricket Teleogryllus oceanicus. Male T. oceanicus use wing stridulation to produce airborne calling songs to attract females and courtship songs to entice females to mate. A new male morph has been discovered, purring crickets, which produce much quieter airborne calling and courtship songs than typical males. Purring males are largely protected from a deadly acoustically orienting parasitoid fly, and they are still able to attract female crickets for mating though typical calling song is more effective for attracting mates. Here, we document the first record of substrate-borne vibration in both typical and purring male morphs of T. oceanicus. We used a paired microphone and accelerometer to simultaneously record airborne and substrate-borne sounds produced during one-on-one courtship trials in the field. Both typical and purring males produced substrate-borne vibrations during courtship that temporally matched the airborne acoustic signal, suggesting that the same mechanism (wing movement) produces both sounds. As previously established, in the airborne channel, purring males produce lower amplitude but higher peak frequency songs than typical males. In the vibrational channel, purring crickets produce songs that are higher in peak frequency than typical males, but there is no difference in amplitude between morphs. Because louder songs (airborne) are preferred by females in this species, the lack of difference in amplitude between morphs in the substrate-borne channel could have implications for mating decisions. This work lays the groundwork for investigating variation in substrate-borne vibrations in T. oceanicus, intended and unintended receiver responses to these vibrations, and the evolution of substrate-borne vibrations over time in conjunction with rapid evolutionary shifts in the airborne acoustic signal.

A novel cricket morph has diverged in song and wing morphology across island populations

“…This lack of preference for specific purring variants suggests that directional selection by female choice is unlikely responsible for the population‐level differences in purring that we show here. In fact, our results may provide support for the ‘signal first’ hypothesis of divergence in animal communication where signals diverge first among groups, followed by the evolution of receiver preferences for these new signal characteristics and ultimately reproductive isolation (Bradbury & Vehrencamp, 2011; Broder, et al, 2021). If preferences for certain purring songs do subsequently develop in females at certain locations but not others, or differences in preferences evolve across populations, divergence among populations could accelerate.…”

“…The residuals of the MANOVA were heavy‐tailed for songs and wings, potentially deviating from normality, so we confirmed results using a nonparametric permutational multivariate analysis of variance with the R package vegan (Oksanen et al, 2022). We included body size (measured as pronotum width; Moradian & Walker, 2008; Broder, et al, 2021; Tan, 2022) in our models because it can impact an individual's song and wing characteristics in some cricket species (Moradian & Walker, 2008; Tan, 2022; Whitman, 2008), and since the purring is generated using an altered instrument with novel wing‐song relationships (Gallagher et al, 2022), we wanted to be sure that any phenotypic differences we found among populations were not simply due to differences in body size. To determine whether there were morphological differences among populations in harp width we used a two‐way analysis of variance (ANOVA) with population, body size, and their interaction as independent variables.…”

More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket

“…This reveals the complexity and synchronisation between multiple signalling mechanisms, including a drumming signal that went completely unnoticed despite decades of study of this model species. Along with the recent discovery of drumming in the Paci c led cricket (Broder et al 2021), this calls for revisiting cricket courtship behaviour, with a speci c focus on vibrational signals that may complement stridulation.…”

“…Simultaneously, an investigation into the vibrational channel in the paci c eld cricket, Teleogryllus oceanicus, revealed a previously unknown drumming signal accompanying the song (Broder et al 2021). Yet, the signal's function remained unclear, as a follow up study showed female preference for nondrumming over drumming individuals (Wikle et al 2023).…”

The persistence and evolutionary consequences of vestigial behaviours

“…Interestingly, recent evidence suggests that this retention of singing motor behaviour in silent crickets could facilitate evolutionary re‐emergence of the sexual signal, perhaps with different acoustic properties (Schneider et al ., 2018; Bailey, Pascoal & Montealegre, 2019). This might be expected in cases where benefits of mate attraction outweigh risks of attracting predators or parasites, or in which ‘clandestine’ communication is possible (Tinghitella et al ., 2018, 2021; Broder et al ., 2021b).…”